Is there any normal, logic reason to explain that? Any except "artistic freedom"? In large gangbangs we have bunch of cock jerkings from the side when at least 1 more guy can join the action and in 4 on 1 there are TPs, TAPs, sometimes even blowjob too = full airtight action, so all guys are in the action.
Also one more interesting thing, I'm wondering are Wakas maybe infected with something? I mean in Blackened scenes, "white" cum is always swallowed and "black" cum always goes on face. Also, lot of Waka Waka scenes with facials only.